The test, sometimes called a cardiotocography, records your baby's movement, heartbeat, and contractions. It notes changes in heart rhythm when your baby goes from resting to moving, or during contractions if you're in labor. Your baby's heart should beat faster when active -- just like yours. The NST can reassure you that your baby is healthy and getting enough oxygen. Show
It's called a nonstress test because the test won’t bother your baby. Your doctor won't use medications to make your baby move. The NST records what your baby is doing naturally. Who Gets the Nonstress Test?NST is a common test for pregnant women. Your doctor may use it to check the health of your baby after weeks 26 to 28 of pregnancy. Certain results may mean your doctor needs to monitor your baby, do more tests, or schedule delivery. You may need an NST if:
What to Expect During a Nonstress TestThe NST is safe for you and your baby. Your doctor will take your blood pressure before the test. Then, you'll lie down with two belts around your belly. One measures your baby's heartbeat and the other measures contractions. (If you’re carrying twins, you’ll have two belts to check their heartbeats.) Your doctor will check your blood pressure from time to time while they test your baby. When you feel the baby kick or move, you may press a button so your doctor can see how the baby's heartbeat changed while moving. The test will take about 20 minutes. If your baby seems to be sleeping, a nurse may try to wake up your baby by ringing a bell, moving your belly, or by using an acoustic stimulator. A normal NST shows that your baby is getting enough oxygen and is doing well. If the results are unusual, your doctor may suggest further testing. You can get one of two results from an NST: Reactive: This result means that your baby’s heart rate went up to the expected level at least twice during the test. Nonreactive: This means your baby’s heart rate didn’t rise as much as expected during the test. It doesn't necessarily mean there’s a problem. You can get this result if your baby is asleep. If your test is nonreactive your doctor may do other tests. If your baby doesn't move during the NST, try not to worry. Many women with nonreactive results turn out to have perfectly healthy babies. Sometimes, babies sleep through the whole thing. The test is not checking "movement," but evaluating reactivity of the heartbeat. There may or may not be appreciable movement during the test. You might start getting weekly or twice weekly nonstress testing after 28 weeks if you have a high-risk pregnancy. (Before 28 weeks, the test isn't accurate.) You may only need one isolated NST if the baby is not moving well. You may need the test more often depending on your situation. Ask your doctor. A test similar to the NST is the contraction stress test. Your doctor may suggest you have this test if you are 34 weeks or more pregnant, and you’ve had a nonreactive result with a NST. SOURCES: Pagana, K.D. Mosby’s Diagnostic and Laboratory Test Reference, 10th ed. Mosby: 2010. ACOG: Special Tests for Monitoring Fetal Health. Johns Hopkins Manual of Gynecology and Obstetrics, 4th Edition. Lippincott Williams & Williams, 2010. Prenatal non-stress test, popularly known as NST, is a method used to test fetal wellbeing before the onset of labor. A prenatal non-stress test functions in overall antepartum surveillance with ultrasound as a part or component of the biophysical profile. The presence of fetal movements and fetal heart rate acceleration is the most critical feature of the non-stress test. It is a non-invasive test used for the surveillance of high-risk pregnancies when the fetus is judged clinically to be at risk for hypoxemia or increased risk of death. This activity reviews the prenatal non stress test, its indications, clinical relevance, and highlights the role of the interprofessional team in the management of the pregnant patient. Objectives:
IntroductionPrenatal non-stress test, popularly known as NST, is a method used to test fetal wellbeing before the onset of labor. A prenatal non-stress test functions in overall antepartum surveillance with ultrasound as a part or component of the biophysical profile. The presence of fetal movements and fetal heart rate acceleration is the most critical feature of the non-stress test. It is a non-invasive test used for the surveillance of high-risk pregnancies when the fetus is judged clinically to be at risk for hypoxemia or increased risk of death. Trained and certified nurses, midwives and physicians should read and interpret the non-stress test. The NST readings are as reactive and none reactive. The non-stress tests can initiate at 26 to 28 weeks. The NST is reactive from 32 weeks. The Non-Stress Test (NST) is an assessment tool used from 32 weeks of gestation to term to evaluate fetal health through the use of electric fetal monitors that continuously record the fetal heart rate (FHR). The test is used to determine if a fetus is at risk for intrauterine death or neonatal complications, usually secondary to high-risk pregnancies or suspected fetal hypoxemia. The frequency of use is based on clinical judgment, but is common because it is non-invasive and presents a low maternal and fetal risk; however, the test does not hold predictive value and only indicates fetal hypoxemia at time of the test. The presence of fetal heart rate acceleration with fetal movement is the principle behind the non-stress test. The NST recognizes the coupling of fetal neurological status to cardiovascular reflex responses. It is one of the factors that tends to disappear earliest during progressive fetal compromise. Interpretation of the nonstress test follows a systematic approach to include: the baseline fetal heart rate, baseline fetal heart rate variability, presence of accelerations, decelerations, and contractions. IndicationsIndications for the prenatal non-stress test include :
ContraindicationsThe non-stress test is not useful in predicting outcomes or determination of fetal wellbeing in patients with acute events such as evolving placental abruption and cord prolapse. Such acute events require prompt clinical evaluation and delivery of fetus as indicated. EquipmentThe electronic fetal monitor (called the cardiotocogram in the United Kingdom and other countries) is the equipment used for the prenatal nonstress test. The modern equipment records fetal heart rate pattern, contractions, fetal cardiac activity, maternal blood pressure and heart rate on a graph. It has a Doppler transducer for fetal heart rate monitoring and a pressure transducer for monitoring of uterine contractions and fetal movement. The transducers are placed on the pregnant abdomen using belts. The equipment is portable and can be placed in small rooms in the office setting and the hospital as needed. Computerized storage and interpretation of FHR records are obtainable with conventional monitors. Computerized cardiotocography provides a more detailed analysis of the fetal heart rate pattern but has not proved superior to the conventional nonstress test. TechniqueThe NST is usually an outpatient procedure. The patient may be seated in a reclining chair and should tilt to the left to ensure supine hypotensive syndrome. Some patients may require monitoring for more than 30 minutes; such patients include those involved in motor vehicle accidents, fall victims, and those with antepartum hemorrhage and decreased fetal movement after hours. In such patients, the NST should be performed in the hospital setting to allow for prolonged monitoring as indicated. The patients' blood pressure should be recorded before the test is begun and then repeated as indicated. Fetal heart rate is monitored using the Doppler ultrasound transducer, and the tocodynamometer is applied to detect uterine contractions or fetal movement. Fetal activity may be recorded by the patient using an event marker or noted by the staff performing the test. The Non-Stress Test (NST) is an assessment tool used from 32 weeks of gestation to term to evaluate fetal health through the use of electric fetal monitors that continuously record the fetal heart rate (FHR). The test is used to determine if a fetus is at risk for intrauterine death or neonatal complications, usually secondary to high-risk pregnancies or suspected fetal hypoxemia. The frequency of use is based on clinical judgment, but is common because it is non-invasive and presents a low maternal and fetal risk; however, the test does not hold predictive value and only indicates fetal hypoxemia at time of the test. The NST involves 20 minutes of monitoring the FHR while assessing the number, amplitude, and duration of accelerations that usually correlate with fetal movement. A normal test result, as defined by the American College of Obstetrics and Gynecologist, is one in which two or more accelerations peak at 15 bpm or more above baseline, each lasting 15 seconds or more, and all occurring within 20 minutes of beginning the test. It is important to note that an abnormal stress test is not always ominous and can occur with a sleeping fetus. If a test is not reactive, FHR should be monitored for at least 40 minutes to account for the fetus sleep cycle, and vibroacoustic stimulation can be used to stimulate fetal movement. Continuous nonreactive NST can indicate central nervous system depression, but further evaluation is necessary, usually in the form of a biophysical profile or contraction stress test. The diagnostic value of NSTs before 32 weeks varies and has high false-positive rates due to the immaturity of the fetal heart. An NST before 24 weeks gestation is nonreactive. A nonreactive NST is one that lacks sufficient fetal heart rate accelerations over 40 minutes. The NST of most preterm fetuses are frequently nonreactive: From 24 weeks, up to 50 percent of NSTs may be nonreactive, and from 28 to 32 weeks of gestation, 15 percent of NSTs are not reactive. For preterm fetuses between 24 weeks and 32 weeks, the predictive value of NSTs has its basis on a lower threshold of acceleration (at least 10 beats per minute from baseline) and has been evaluated and found to sufficiently predict fetal wellbeing. Clinical SignificanceThe non-stress test is one of the most widely used techniques for antepartum fetal evaluation. Antepartum fetal surveillance techniques are used to assess the risk of fetal death in pregnancies complicated by preexisting maternal conditions (e.g., diabetes mellitus) as well as those in which complications have developed (e.g., fetal growth restriction).. The presence of fetal heart rate acceleration with fetal movement is the principle behind the none stress test. The NST recognizes the coupling of fetal neurological status to cardiovascular reflex responses. It is one of the factors that tends to disappear earliest during the progressive fetal compromise.. The interpretation of the non-stress test is as reactive or none reactive. The criteria for a reactive NST are at least two FHR accelerations lasting at least 15 seconds and rising at least 15 beats/minute above the established baseline heart rate. Most term fetuses have many of these accelerations in each 20- to 30- minute period of active sleep, and the term fetus seldom goes more than 60 minutes, and certainly not more than 100 minutes without meeting these criteria. When the non-stress test is not reactive, It should be extended to another 20 minutes in an attempt to separate the fetus in a period of prolonged quiet sleep from those who are hypoxemic or asphyxiated. Vibroacoustic stimulation (VAS) may be used to change fetal state from quiet to active sleep and shorten the length of the NST. If the NST remains nonreactive after 60 minutes. The fetus should undergo evaluation with an ultrasound biophysical profile. In three studies, about 3 percent of fetuses tested remained nonreactive after 80 to 90 minutes of testing. Two stillbirths and one neonatal death occurred in seven cases of prolonged absence of reactivity. DOcumentation showed IUGR in 74 percent of cases, oligohydramnios in 81 percent, fetal acidosis in 41 percent, and placental infarction in 93 percent. If the NST is an extended examination, and there is an observable, persistent absence of reactivity, the fetus is likely to be severely compromised. Preterm fetuses, fetuses with intrauterine growth restriction at similar gestation, fetuses with maternal medications such as sedatives and magnesium sulfate frequently have paired accelerations-movement that do not meet these criteria. Falsely reactive NSTs occur at a rate of four to five per 1000 in the largest studies. These occur in asymmetric IUGR, oligohydramnios, or metabolic problems associated with fetal macrosomia for whom false-reassuring rates may reach 15%. Thus, NST has significant liabilities in the groups at highest risk. Strong evidence, including data from randomized trials, shows that practitioners should not rely on the NST in isolation when determining the antenatal status of such fetuses. The nonreactive NST is, by definition, an FHR monitoring interval that does not meet the criteria above. There is variation in the total duration allowed for NST. It ranges from 20 minutes recommended by ACOG to 40 minutes and even 60 minutes by some authors. The most common explanation for a nonreactive NST is the presence of a longer than average sleep cycle in a normal fetus. A nonreactive NST, especially if variability remains present and there are no decelerations, should not be assumed to indicate fetal compromise. The present standard of care is to conduct an ultrasound evaluation with a full biophysical profile. NST in isolation has seen frequent use for post-term pregnancies. However, the presence of decreased fetal movement in post-term pregnancies indicates a more comprehensive evaluation with full ultrasound biophysical profile. Fetal heart rate acceleration may be absent during a period of quiet fetal sleep. Studies demonstrated that the longest time between successive acceleration in the healthy term fetus is approximately 40 minutes. However, the fetus may fail to exhibit heart rate accelerations for up to 80 minutes and still be normal. CNS depressants such narcotics, phenobarbital, magnesium sulfate and beta blockers such as propranolol can reduce fetal heart rate reactivity. Fetal heart rate accelerations also demonstrate decreases in smokers. Variability, constant fluctuations form baseline FHR, as well as decelerations, slowing of FHR, can also be detected on NST. Moderate variability has an amplitude that ranges from 6 to 25 beats per minute and is an indication of a healthy nervous system. Decelerations that are nonrepetitive, and last less than 30 seconds, do not require intervention. Deviation from these guidelines can be associated with fetal compromise and require further evaluation. Enhancing Healthcare Team OutcomesNo trial has conclusively proven that antenatal testing lowers long-term adverse neurologic outcomes so that recommendations might have a rating level of consensus, expert opinion, but no clear evidence. The standard of care can only be a suggestion and probably varies considerably from region to region. The prenatal nonstress test has utility in isolation in post-term pregnancies and patients with decreased fetal movement. When the non-stress test is not reactive, the testing period should extend another 20 minutes in an attempt to delineate between the fetus in a period of prolonged quiet sleep from those who are hypoxemic or asphyxiated. Vibroacoustic stimulation (VAS) may be used to change fetal state from quiet to active sleep and shorten the length of the NST. If the NST remains nonreactive after 60 minutes. The fetus should undergo evaluation with an ultrasound biophysical profile. Interpretation of the nonstress test should always take into consideration individual patient clinical condition, gestational age, and associated maternal comorbidities. The clinician should not hesitate to perform the further evaluation with the biophysical profile, Doppler ultrasound for umbilical artery evaluation, continuous fetal monitoring, consultation with maternal and fetal medicine specialists, admission to the hospital and delivery of the fetus as indicated. References1.Preboth M. ACOG guidelines on antepartum fetal surveillance. American College of Obstetricians and Gynecologists. Am Fam Physician. 2000 Sep 01;62(5):1184, 1187-8. [PubMed: 10997537] 2.Sharma J, Goyal M. Cardiotocography and diabetic pregnancy. 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Ultrasound Obstet Gynecol. 2007 Oct;30(5):750-6. [PubMed: 17688309] 11.Lavin JP, Miodovnik M, Barden TP. Relationship of nonstress test reactivity and gestational age. Obstet Gynecol. 1984 Mar;63(3):338-44. [PubMed: 6700856] 12.Brown R, Patrick J. The nonstress test: how long is enough? Am J Obstet Gynecol. 1981 Nov 15;141(6):646-51. [PubMed: 7315894] 13.Keegan KA, Paul RH, Broussard PM, McCart D, Smith MA. Antepartum fetal heart rate testing. V. The nonstress test--an outpatient approach. Am J Obstet Gynecol. 1980 Jan 01;136(1):81-3. [PubMed: 7352491] 14.Keegan KA, Paul RH. Antepartum fetal heart rate testing. IV. The nonstress test as a primary approach. Am J Obstet Gynecol. 1980 Jan 01;136(1):75-80. [PubMed: 6444346] 15.Patrick J, Carmichael L, Chess L, Staples C. Accelerations of the human fetal heart rate at 38 to 40 weeks' gestational age. Am J Obstet Gynecol. 1984 Jan 01;148(1):35-41. [PubMed: 6691379] 16.Gagnon R, Hunse C, Carmichael L, Fellows F, Patrick J. Human fetal responses to vibratory acoustic stimulation from twenty-six weeks to term. Am J Obstet Gynecol. 1987 Dec;157(6):1375-81. [PubMed: 3425645] 17.Visser GH, Sadovsky G, Nicolaides KH. Antepartum heart rate patterns in small-for-gestational-age third-trimester fetuses: correlations with blood gas values obtained at cordocentesis. Am J Obstet Gynecol. 1990 Mar;162(3):698-703. [PubMed: 2316573] 18.Castillo RA, Devoe LD, Arthur M, Searle N, Metheny WP, Ruedrich DA. The preterm nonstress test: effects of gestational age and length of study. Am J Obstet Gynecol. 1989 Jan;160(1):172-5. [PubMed: 2912079] 19.Manning FA, Platt LD, Sipos L. Antepartum fetal evaluation: development of a fetal biophysical profile. Am J Obstet Gynecol. 1980 Mar 15;136(6):787-95. [PubMed: 7355965] 20.Druzin ML, Gratacos J, Paul RH. Antepartum fetal heart rate testing. VI. Predictive reliability of "normal" tests in the prevention of antepartum death. Am J Obstet Gynecol. 1980 Jul 15;137(6):746-7. [PubMed: 7395945] 21.Freeman RK, Anderson G, Dorchester W. A prospective multi-institutional study of antepartum fetal heart rate monitoring. I. Risk of perinatal mortality and morbidity according to antepartum fetal heart rate test results. Am J Obstet Gynecol. 1982 Aug 01;143(7):771-7. [PubMed: 7102744] 22.Ivanov B, Malinova M. [Comparative study of pathological Doppler and non-stress test in IUGR]. Akush Ginekol (Sofiia). 2011;50(7):12-6. [PubMed: 22452172] 23.Leveno KJ, Williams ML, DePalma RT, Whalley PJ. Perinatal outcome in the absence of antepartum fetal heart rate acceleration. Obstet Gynecol. 1983 Mar;61(3):347-55. [PubMed: 6823377] 24.Nochimson DJ, Turbeville JS, Terry JE, Petrie RH, Lundy LE. The nonstress test. Obstet Gynecol. 1978 Apr;51(4):419-21. [PubMed: 662223] 25.Schifrin BS, Foye G, Amato J, Kates R, MacKenna J. Routine fetal heart rate monitoring in the antepartum period. Obstet Gynecol. 1979 Jul;54(1):21-5. [PubMed: 450360] 26.Margulis E, Binder D, Cohen AW. The effect of propranolol on the nonstress test. Am J Obstet Gynecol. 1984 Feb 01;148(3):340-1. [PubMed: 6695981] 27.Phelan JP. Diminished fetal reactivity with smoking. Am J Obstet Gynecol. 1980 Jan 15;136(2):230-3. [PubMed: 7352504] 28.Keegan KA. The nonstress test. Clin Obstet Gynecol. 1987 Dec;30(4):921-35. [PubMed: 3319323] 29.Unterscheider J, Daly S, Geary MP, Kennelly MM, McAuliffe FM, O'Donoghue K, Hunter A, Morrison JJ, Burke G, Dicker P, Tully EC, Malone FD. Definition and management of fetal growth restriction: a survey of contemporary attitudes. Eur J Obstet Gynecol Reprod Biol. 2014 Mar;174:41-5. [PubMed: 24360357] Does everyone get a non stress test during pregnancy?Not everyone needs a nonstress test. Your pregnancy care provider orders a nonstress test to check fetal health. Some reasons they may do this include: You're past your due date: You're overdue once your pregnancy is past 40 weeks.
Why is a non stress test done during pregnancy?A nonstress test (NST) is usually done when a health care provider wants to check on the health of the fetus, such as in a high-risk pregnancy or when the due date has passed. The test checks to see if the baby responds normally to stimulation and is getting enough oxygen.
What week is the stress test during pregnancy?When Are Contraction Stress Tests Done? A contraction stress test can be done at 34 weeks or later.
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